1. Field of the Invention
The present invention relates to a radar apparatus for vehicle and a method of removing a ghost of the radar apparatus for vehicle, and more particularly to a radar apparatus and a method of removing a ghost by determining a grating lobe ghost based on a reception signal received through linearly and equally spaced receiving antennas and unequally spaced receiving antennas.
2. Description of the Prior Art
Recently, the utilization of a driver safety system based on a radar for preventing a clash of vehicles and for safe driving has been gradually expanded. The driver safety system should measure information, such as the distances and the speeds of each target, required from the driver safety system in a high accuracy, although there are a plurality of targets.
Generally, a radar apparatus for vehicle used in the driver safety system uses a phased array antenna technology due to a limit of a space where the radar apparatus is installed in the vehicle.
In the phased array antenna, a digital beamforming and an angle estimating method use a method of using phases of each channel, which is different according to an angle formed by a receiving an antenna and a target.
However, when an interval between the receiving antennas is higher than a half wavelength, an angle of a target may be ambiguous according to a repetition of a phase. Therefore, in addition to an angle estimation, a target outside of FoV has a gain equal to that of a target in the FoV and an Angular Power Spectrum (APS) form similar to that of the target in the FoV as shown in FIG. 1, and thus the target outside of the FoV is detected as a ghost target. This is referred to as a grating lobe ghost.
In the radar apparatus for vehicle, a grating lobe ghost as shown in FIG. 2 may cause an error in a target sensing during driving.
Although a reception power of a target in a FoV is different from that of a target outside of the FoV according to the directivity of a transmitting antenna and a receiving antenna, it is not easy for the existing radar apparatus for the vehicle to determine a grating lobe ghost since there are targets having various RCSs from a pedestrian to a truck on a road.
The existing radar apparatus for a vehicle has problems, such as an SNR reduction due to a clutter outside the FoV and an angle resolution performance reduction, since a main beam becomes wide in the case of the beamforming when an interval of antennas becomes narrow close to a half wavelength in order to remove the grating lobe ghost.